Critical to the occurrence of a LTP/VLTP is that some helium survives the merger process.
When two WDs merge in the DD scenario the helium, which one or two of them have, easily burns because of the high temperatures that the outer zones achieve (e.g., [1]}, [2]}, [3]}, [4]}). Therefore, it is not clear at all whether any helium can survive the merger of two WDs. The answer will come from future 3D simulations.
